Coated strain-hardened metal



UNITED STATES PATENT oEEicE.

WILLIS R. WHITNEY, 0E msxarnm, NEW Yonx, nssrenon. '10 GENERAL ELECTRICcomm, A conrona'rron on NEW Yonx.

COATED STBAiN-HAB-DENED METAL.

No Drawing.

To all whom it may concern:

Be it known that I, WILLIS R. Wnrrnnr, a citizen of the United States,residing at Niskayuna in the county of Schenectady,

State of New York, have invented certain likewise greatly reduced thetensile strength.

Experiments which have been made indicate that the deleterious effect isconnected in some way with the generation of'hydrogen at the surface ofthe ferrous metal.

I have discovered that this deleterious effect may be obviated byproviding metal under strain before being subjected to ahydrogen-generating bath, with a coating of material which issubstantially impervious to nascent hydrogen, for example, metallic tin.The metal thus coated may subsequently be electro-plated without anydeleterious effects upon its mechanical proper ties.

In carrying out my invention which includes both a process and a newarticle resultin therefrom, the metal to be coated is pre erably firstcleaned mechanically, for example, by sand blasting, and is then dipped,in the presence of a suitable flux, into a coating metal. When thustreating a metal such as spring steel which has been given a temper orset under strain, it is necessary that a plating material should'bechosen which has a melting point below the temperature at which themetal has been tem ered. In case of sprin steel the tempermg tem ratureis somew ere about 300 0. As tin as a melting point of 232" and as itcan readily adhere to a clean surface of ferrous metal, it isparticularly well suited for the purpose of my invention. The

' cleaned steel springs or other strain-hardened articles to be coated,may be d pped Specification of Letters Patent.

sequent c Patented Feb. 24, 1920.

Application filed June 15, 1918. Serial No. 240,177.

into the tin bath in the resence of rosin or other suitable flux.ubsequent to the tinning operation the steel articles may beelectroplated in the usual way, for example, with copper, withoutimpairing their mechanical properties.

The followin specific figures will illustrate the bene ts of myinvention. Two steel springs were selected from a lot of springs,samples of which upon test had broken on the testing machine with a ullvarying between 310 and 439 pounds. he selected test springs were madecathode for one-half hour a copper cyanid solution and when tested werefound to break at 69 and 137 pounds pull respectively. 'The electrolytictreatment had reduced the breaking strength to about 22% and 31%respectively, of the average value of strength of similar untreated spFurthermore, the copper plated samp es stretched very little before theybroke, while the untreated stretched one or two times their originallength. Two more test springs were pickled respectively for threeminutes and one hour in a 20% sulfuricacid solution. The sample pickledfor three minutes broke at 198 pounds showing a reduction of strength to50% of the untreated value and the second sample pickled for one hour,broke at 29 pounds with a reduction in strength to 7% ofthe untreatedvalue. The latter sample had been reduced by but one-thousandth of aninch in diameter by the action of the acid, which clearly shows thatdiminution of size does not account for the weakening of the metal.

Additional samples of steel springs were first sand blasted, dipped intomolten resin and then into molten tin heated to a temperature of about260 to 300 C. After having been tinned the samples were copper plated inthe same solution used for copper plating the test samples abovedescribed. These tin plated samp es showed a breaking strength rangingfrom 318 to 417' pounds, all

strength values obtained for the untreated springs, In other words, themechanical properties of the samples had not been appreciablyaffected bythe tin treatment and these properties were retained during asubectrolytic treatment.

. Although I have described the benefits of my'invention with particularreference to strained spring steel, I desire it to be under stood thatmy invention is also a plicable with beneficial result to other f drmsof strain-hardened, steel, for example, steel articles of various sortswhich have been formed by cold ressi or otherwise strained beyond theirelastic limit.

What I claim as new and desire to secure 4 by Letters Patent ofthe-United States, is

1. The process of reventing ferrous metal while under strain rombecoming brittle by .the action of a hydrogen-generating agent.

which consists in providing said metal with a coating of material whichis substantially impermeable to hydrogen, and then subjecting the metalto said agent. 4

I 2. he process of electroplating strainhardened ferrous metal whichconsists in v first providing said metahwith .a coating of conductivematerial such as tin impermeable to nascent hydrogen whilepreventingelectrolytic action, andthen subjecting to a desired electro-platingtreatment.

3. The process of preventing strain-hardened steel from becomin brittleby the action of an electrolytic bat which consists in roviding saidsteel with a coating of tin while preventing the generation of hydrogenat the surface of said steel, and then subjecting the coated steel tothe desired electrolytic treatment.

' 4. The process of plating strain-hardened steel by. electrolysis whichconsists in applying to said steel a coating of tin in the absence of anagent generatlng'hydrogen, and then applying a desired metal byelectroly- SIS.

5 The process of coating steel springs which consistsin mechanicallycleaning said springs, applying a ,coating of tin in the presence of areslnous flux and then applying a desired coating of metal by electroly-SIS. K

' 6. An article of manufacture comprising ferrous spring metal, acoating of tin thereon and a coating of electro-deposited metal uponsaid tin, said metal having substantially the same mechanical .ropertiesas unplated metal of the same 0 aracter.

7. An article of manufacture, comprising a steel spring, a coating oftin thereon, and a coating of electro-deposited copper upon said tin,said spring having substantially the same mechanical PI'QPQIQIGS asunplated steel of the same character.

8. An article of manufacture, comprising a strain-hardened ferrousmetal, a coating of conductive material substayally imper- "meable tohydrogen upon sai

